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Register a new userMapping the Periphery and Variability of the Magellanic Clouds
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We propose a combination of a modified Wide-Fast-Deep survey, a mini-survey of the South Celestial Pole, and a Deep Drilling-style survey to produce a 3-D map of the Magellanic System and to provide a detailed census of the transient and variable populations in the Clouds. We support modifying the Wide-Fast-Deep survey to cover the declination range $-72.25deg<{rm Dec}<12.4deg$ and the Galactic latitude range $|b|>15deg$, as proposed in a separate white paper. We additionally propose a mini-survey covering the 950$deg^2$ with ${rm Dec} < -72.25$ in $ugriz$ to the standard LSST single-exposure depth and with 40 visits per filter per field. Finally, we propose a mini-survey covering $sim100 deg^2$ of the main bodies of the Clouds with twelve total pointings, 2000 total visits per field, and shorter exposure time.
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We provide a homogeneous set of structural parameters of 83 star clusters located at the periphery of the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). The clusters stellar density and surface brightness profiles were built from deep, AO assisted optical images, and uniform analysis techniques. The structural parameters were obtained from King and Elson et al. model fittings. Integrated magnitudes and masses (for a subsample) are also provided. The sample contains mostly low surface brightness clusters with distances between 4.5 and 6.5 kpc and between 1 and 6.5 kpc from the LMC and SMC centres, respectively. We analysed their spatial distribution and structural properties, comparing them with those of inner clusters. Half-light and Jacobi radii were estimated, allowing an evaluation of the Roche volume tidal filling. We found that: (i) for our sample of LMC clusters, the tidal radii are, on average, larger than those of inner clusters from previous studies; (ii) the core radii dispersion tends to be greater for LMC clusters located towards the southwest, with position angles of $sim$200 degrees and about $sim$5 degrees from the LMC centre, i.e., those LMC clusters nearer to the SMC; (iii) the core radius evolution for clusters with known age is similar to that of inner clusters; (iv) SMC clusters with galactocentric distances closer than 4 kpc are overfilling; (v) the recent Clouds collision did not leave marks on the LMC clusters structure that our analysis could reveal.
We present the first results from the SAGE-Var program, a follow on to the Spitzer legacy program Surveying the Agents of Galaxy Evolution (SAGE; Meixner, et al. 2006). We obtained 4 epochs of photometry at 3.6 & 4.5 microns covering the bar of the Large Magellanic Cloud (LMC) and the central region of the Small Magellanic Cloud (SMC) in order to probe the variability of extremely red sources missed by variability surveys conducted at shorter wavelengths, and to provide additional epochs of observation for known variables. Our 6 total epochs of observations allow us to probe infrared variability on 15 different timescales ranging from ~20 days to ~5 years. Out of a full catalog of 1,717,554 (LMC) and 457,760 (SMC) objects, we find 10 (LMC) and 6 (SMC) large amplitude AGB variables without optically measured variability owing to circumstellar dust obscuration. The catalog also contains multiple observations of known AGB variables, type I and II Cepheids, eclipsing variables, R CrB stars and young stellar objects which will be discussed in following papers. Here we present infrared Period-Luminosity (PL) relations for classical Cepheids in the Magellanic Clouds, as well as improved PL relationships for AGB stars pulsating in the fundamental mode using mean magnitudes constructed from 6 epochs of observations.
We study the morphology of the stellar periphery of the Magellanic Clouds in search of substructure using near-infrared imaging data from the VISTA Hemisphere Survey (VHS). Based on the selection of different stellar populations using the ($J-K_mathrm{s}$, $K_mathrm{s}$) colour-magnitude diagram, we confirm the presence of substructures related to the interaction history of the Clouds and find new substructures on the easter side of the LMC disc which may be owing to the influence of the Milky Way, and on the northern side of the SMC, which is probably associated to the ellipsoidal structure of the galaxy. We also study the luminosity function of red clump stars in the SMC and confirm the presence of a bi-modal distance distribution, in the form of a foreground population. We find that this bi-modality is still detectable in the eastern regions of the galaxy out to a 10 deg distance from its centre. Additionally, a background structure is detected in the North between 7 and 10 deg from the centre which might belong to the Counter Bridge, and a foreground structure is detected in the South between 6 and 8 deg from the centre which might be linked to the Old Bridge.
Despite their close proximity, the complex interplay between the two Magellanic Clouds, the Milky Way, and the resulting tidal features, is still poorly understood. Recent studies have shown that the Large Magellanic Cloud (LMC) has a very extended disk strikingly perturbed in its outskirts. We search for recent star formation in the far outskirts of the LMC, out to ~30 degrees from its center. We have collected intermediate-resolution spectra of thirty-one young star candidates in the periphery of the LMC and measured their radial velocity, stellar parameters, distance and age. Our measurements confirm membership to the LMC of six targets, for which the radial velocity and distance values match well those of the Cloud. These objects are all young (10-50 Myr), main-sequence stars projected between 7 and 13 degrees from the center of the parent galaxy. We compare the velocities of our stars with those of a disk model, and find that our stars have low to moderate velocity differences with the disk model predictions, indicating that they were formed in situ. Our study demonstrates that recent star formation occurred in the far periphery of the LMC, where thus far only old objects were known. The spatial configuration of these newly-formed stars appears ring-like with a radius of 12 kpc, and a displacement of 2.6 kpc from the LMCs center. This structure, if real, would be suggestive of a star-formation episode triggered by an off-center collision between the Small Magellanic Cloud and the LMCs disk.
Diffuse interstellar bands (DIBs) trace warm neutral and weakly-ionized diffuse interstellar medium (ISM). Here we present a dedicated, high signal-to-noise spectroscopic study of two of the strongest DIBs, at 5780 and 5797 AA, in optical spectra of 666 early-type stars in the Small and Large Magellanic Clouds, along with measurements of the atomic Na,{sc i},D and Ca,{sc ii},K lines. The resulting maps show for the first time the distribution of DIB carriers across large swathes of galaxies, as well as the foreground Milky Way ISM. We confirm the association of the 5797 AA DIB with neutral gas, and the 5780 AA DIB with more translucent gas, generally tracing the star-forming regions within the Magellanic Clouds. Likewise, the Na,{sc i},D line traces the denser ISM whereas the Ca,{sc ii},K line traces the more diffuse, warmer gas. The Ca,{sc ii},K line has an additional component at $sim200$--220 km s$^{-1}$ seen towards both Magellanic Clouds; this may be associated with a pan-Magellanic halo. Both the atomic lines and DIBs show sub-pc-scale structure in the Galactic foreground absorption; the 5780 and 5797 AA DIBs show very little correlation on these small scales, as do the Ca,{sc ii},K and Na,{sc i},D lines. This suggests that good correlations between the 5780 and 5797 AA DIBs, or between Ca,{sc ii},K and Na,{sc i},D, arise from the superposition of multiple interstellar structures. Similarity in behaviour between DIBs and Na,{sc i} in the SMC, LMC and Milky Way suggests the abundance of DIB carriers scales in proportion to metallicity.
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